ABSTRACT
Concrete durability is significantly affected by water transport because many of the most important damage processes take place in concrete with water. A profound understanding of water transport in porous concrete is therefore of central importance to assess its durability performance. While water uptakes (imbibitions) in concrete are commonly observed in our daily life, tracing the water imbibition paths remain a big challenge. An important reason is that it is difficult to probe the water confined in concrete matrix with complex and heterogeneous microstructure. In the present study, we attempted to trace the water imbibition in concrete by transmission X-ray radiography (TXR) with caesium chloride (CsCl) enhancing technique combined with SEM-BSE/EDS test. Because of the high X-ray attenuation of Cs, the contrast gradients of TXR images for partially saturated concrete can be greatly improved with the CsCl enhancement. Slice samples were prepared for TXR tests to obtain high-resolution X-ray phase images. Aqueous solutions containing different concentrations of CsCl were used as the liquid agents for imbibition tests. X-ray scans were performed on the samples to probe imbibition processes. SEM-BSE/EDS tests were performed to measure the compositional changes of concrete slices. Results shows that water penetration paths and fronts can be more clearly observed in TXR images when CsCl enhancement was applied. The CsCl enhancement also increases the contrast gradient of SEM-BSE images, and the trace of Cs by EDS facilitates the determination of liquid penetration fronts. The findings of this study provide new insights in characterizing water transport in concrete.
